A method for reducing chlorine-containing impurities in isocyanates

Abstract

This invention relates to a method for reducing chlorine impurities in isocyanates. The method includes a step of hydrodechlorinating a crude isocyanate product obtained by the phosgene process with hydrogen in the presence of a catalyst. The crude isocyanate product contains chlorine impurities. The catalyst is a supported catalyst and includes a support, an active component, and an auxiliary agent. The active component is a Group VIII metal, and the auxiliary agent is selected from one or more combinations of Ag, Cu, Sn, Zn, Cd, In, Ba, K, and Au. Preferably, the support is a basic anion exchange resin with quaternary ammonium functional groups. This method can effectively reduce the content of chlorine impurities in the crude isocyanate product, reduce the hydrolyzed chlorine content and color of the isocyanate product, and also reduce the acidity of the isocyanate product.

Description

Technical Field

[0001] This invention specifically relates to a method for reducing chlorine-containing impurities in isocyanates. Background Technology

[0002] Isocyanates are one of the important raw materials for the preparation of polyurethane materials. Currently, large-scale production of isocyanates typically employs the phosgene process, which involves the phosgenation of relevant amines, followed by the removal of phosgene and solvents, and purification to obtain the isocyanate product. While the phosgene process is technically mature and economically viable, it is prone to producing chlorinated byproducts. The phosgenation process introduces various chlorine-containing impurities such as carbamoyl chlorides and chlorinated aromatic hydrocarbons, resulting in residual hydrolyzable chlorinated byproducts in the isocyanate product, affecting product quality and color. Therefore, reducing the content of chlorine impurities in isocyanate products to obtain light-colored isocyanates with excellent color is a pressing issue in isocyanate synthesis.

[0003] European patent EP0546398 describes acidifying the raw material 4,4′-diaminodiphenylmethane (MDA) for the synthesis of diphenylmethane diisocyanate (MDI) with hydrochloric acid before the phosgenation reaction. European patent EP0446781 describes treating the raw material 4,4′-diaminodiphenylmethane (MDA) for the synthesis of isocyanate with hydrogen before the phosgenation reaction. The purpose of both is to reduce the content of chlorine impurities in the product, thereby obtaining a light-colored MDI.

[0004] US Patent 4465639 reduces the color of the crude isocyanate product by adding water after the phosgenation reaction. European Patents EP0445602 and EP0467125 add alkanols or polyether polyols after the phosgenation reaction to remove chlorine-containing impurities that contribute to color development, thereby lightening the color of the isocyanate product.

[0005] Chinese patent CN112430295B discloses the use of a dechlorination agent to treat isocyanate products. This dechlorination agent can adsorb and dissociate hydrogen chloride and acyl chloride in the product, thereby reducing the hydrolyzable chlorine content and color of the isocyanate product.

[0006] It is evident that existing technologies, in order to reduce the content of chlorine impurities in isocyanate products and decrease their color, typically control the impurity content in the chlorine gas used in the synthesis of phosgene, or treat the crude isocyanate product to reduce the content of chlorine impurities, thereby reducing the product's color and the content of hydrolyzed chlorine. However, both of these methods have certain limitations. Adding a treatment agent to the crude isocyanate product inevitably introduces new impurities, reducing product purity and NCO content. Furthermore, chlorine impurities mainly originate from the phosgenation reaction, and controlling or treating the raw amines or phosgene has limited effectiveness. Summary of the Invention

[0007] The purpose of this invention is to provide a method for reducing chlorine impurities in isocyanates. This method can effectively reduce the content of chlorine impurities in crude isocyanate products, reduce the hydrolyzed chlorine content and color of isocyanate products, and also reduce the acidity of isocyanate products.

[0008] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0009] A method for reducing chlorine-containing impurities in isocyanates, the method comprising the step of hydrodechlorinating a crude isocyanate product obtained by the phosgene process with hydrogen in the presence of a catalyst, wherein the crude isocyanate product contains chlorine-containing impurities, the catalyst is a supported catalyst and comprises a support, an active component and an auxiliary agent, wherein the active component is a Group VIII metal, and the auxiliary agent is selected from one or more combinations of Ag, Cu, Sn, Zn, Cd, In, Ba, K and Au.

[0010] In the phosgene process for isocyanate preparation, amines and phosgene, or amine solutions and phosgene solutions, react to synthesize isocyanates. The reactants, target products, and byproducts exist in the reaction system in gaseous and / or liquid forms, respectively. When preparing isocyanates using the phosgene process, excess phosgene is typically removed from the reaction system first, followed by the removal of a large amount of solvent, yielding crude isocyanate. Because the phosgene process generates chlorine-containing impurities such as carbamoyl chloride and chlorinated aromatic hydrocarbons, the crude isocyanate product contains these chlorine-containing impurities. In this invention, chlorine-containing impurities refer to all impurities containing chlorine that may be present in the crude isocyanate product.

[0011] In this invention, Group VIII metals include iron group metals, specifically iron, cobalt, and nickel. Group VIII metals also include platinum group metals, specifically platinum (Pt), palladium (Pd), osmium (Os), iridium (Ir), ruthenium (Ru), and rhodium (Rh).

[0012] To reduce the chlorine impurity content in crude isocyanate products and obtain lighter-colored isocyanate products, existing technologies typically involve adding various treatment agents to process the crude isocyanate products or controlling the chlorine impurity content in the raw materials. However, the inventors of this application have discovered a novel method to reduce the chlorine impurity content in crude isocyanate products. This involves subjecting the crude isocyanate product to a hydrodechlorination reaction with hydrogen in the presence of a catalyst. This allows chlorine impurities in the crude product, such as carbamoyl chloride and chlorinated aromatics, to react with hydrogen to generate chlorine-free organic compounds and HCl. Furthermore, the selection of the catalyst composition allows it to adsorb HCl gas, further shifting the hydrodechlorination reaction in the forward direction and further reducing the chlorine impurity content. Simultaneously, it also reduces the acidity of the isocyanate product.

[0013] Group VIII metals are commonly used active components in hydrogenation catalysts. Their catalytic hydrogenation and dechlorination mechanism is as follows: H2 is activated into hydrogen atoms on the surface of the active center of the catalyst supported by noble metals or transition metals. Under the action of the catalyst, the C-Cl bond in the organic chlorine-containing impurities is activated and reacts with the activated hydrogen atoms to convert into HCl.

[0014] The inventors of this application discovered through research that by doping a suitable metal promoter into a Group VIII metal catalyst, the surface electron cloud and surface chemical properties of the promoter (co-catalyst) symbiotic alloy with the active metal change, thereby enhancing the adsorption energy of hydrogen, organic chlorine-containing impurities, and reaction intermediates on the catalyst surface. This results in the active metal nanoparticles exhibiting higher selectivity, conversion rate, and catalytic performance, and the bimetallic catalyst exhibits higher catalytic activity and stability than the monometallic catalyst.

[0015] For example, adding a metal co-catalyst to a Pd catalyst can benefit the active center Pd. 0 Maintaining the valence state has a promoting effect, that is, effectively limiting the oxidation of Pd at the catalytic active center and increasing the valence state of Pd. 0 / Pd 2+ The ratio, and thus Pd 0 The active center more effectively activates the Cl-C chemical bond, reducing its bond energy. The addition of the promoter significantly improves the dispersion and loading rate of the active metal particles, effectively enhancing the initial activity and reaction efficiency of the hydrodechlorination reaction. The initial activity and reaction efficiency of the catalyst regulated by the promoter are significantly higher than those of the single-metal catalyst without the addition of the promoter.

[0016] In some embodiments, the active component is selected from one or more combinations of Pd, Pt, Rh, Ru, and Ni.

[0017] In some embodiments, the active component is selected from Pd, Pt, or Ni; and the auxiliary agent is selected from Ag, Cu, or Sn.

[0018] Adding a certain amount of Sn increases the dispersion and specific surface area of ​​Pd, thereby enhancing the catalyst's catalytic activity. Both the active components Pd and Ni exhibit strong electronic interactions and form ultrafine nanoparticles on the support, contributing to the catalyst's high catalytic activity and stability. When Ag is used as the promoter, isolated Pd species surrounded by Ag exist in the bimetallic catalyst, enhancing the activity of both Ag and Pd species and promoting the breaking of C-Cl bonds. K, as an electronic promoter, increases the electron cloud density around Pd, which is beneficial for C-Cl bond breaking. The hydrodechlorination catalyst with noble metal Pd as the active component exhibits high catalytic activity, selectivity, and stability, and the addition of the specific type of promoter metal of this invention can further enhance its catalytic activity and stability.

[0019] In some embodiments, the carrier is a basic anion exchange resin. Compared with inorganic carriers, resin carriers are easier to control in terms of metal loading and dispersion uniformity by manipulating the adsorption isotherm of the metal. Furthermore, resin carriers exhibit stronger resistance to organic contamination and chlorine poisoning, lower metal leaching rates, and longer service life. Simultaneously, resin carriers can also adsorb HCl gas generated during the hydrodechlorination reaction, thereby reducing the acidity of the isocyanate product.

[0020] In some embodiments, the carrier is a basic anion exchange resin with quaternary ammonium functional groups. Basic anion exchange resins with quaternary ammonium functional groups can better promote the smooth progress of the hydrodechlorination reaction and more effectively reduce the chlorine impurity content of the crude isocyanate product.

[0021] In some embodiments, the carrier is selected from one or more combinations of Diaion PA308 resin, Dowex MSA-1 resin, and Lewait MP 500 resin.

[0022] In some embodiments, the catalyst contains 0.01% to 3% of the active component and 0.03% to 8% of the additives by weight percentage.

[0023] In some embodiments, the catalyst contains 0.05% to 2% of the active component and 0.1% to 5% of the additives by weight percentage.

[0024] In some embodiments, the catalyst is prepared by reducing a precursor of the active component and a precursor of an auxiliary agent loaded on a support.

[0025] In some embodiments, the precursor of the active component is selected from one or more combinations of nitrates, acetates, chlorides, chlorometallic acids, and acetylacetone metal compounds of the active component.

[0026] In some embodiments, the precursor of the adjuvant is selected from one or more combinations of nitrates, acetates, and chlorides of the adjuvant.

[0027] In some embodiments, the precursor of the active component is selected from palladium nitrate, palladium acetate, chloroplatinic acid, ruthenium trichloride, iridium trichloride, rhodium trichloride, cobalt nitrate, nickel nitrate, or nickel acetylacetonate.

[0028] In some implementations, the loading is performed by impregnation.

[0029] In some embodiments, the reduction reaction is carried out in the presence of a reducing agent selected from one or more combinations of sodium borohydride, hydrazine hydrate, hydrogen gas, and sodium sulfite.

[0030] In some embodiments, the temperature of the hydrodechlorination reaction is 50–150°C.

[0031] In some embodiments, the mass ratio of the crude isocyanate product to hydrogen is 10000:1 to 1000:1.

[0032] In some embodiments, the hydrodechlorination reaction is carried out in a reactor, which is selected from a batch reactor, a fixed-bed reactor, a fluidized-bed reactor, or a tower reactor.

[0033] In some embodiments, the reactor is a fixed-bed reactor, and the volume hourly space velocity of the catalyst is 500–2000 h⁻¹. -1 .

[0034] In some embodiments, the reactor is selected from a batch reactor, a fluidized bed reactor, or a tower reactor, and the mass of the catalyst is 0.05 to 2% of the mass of the crude isocyanate product.

[0035] In some embodiments, the isocyanate is selected from aliphatic or aromatic isocyanates.

[0036] In some embodiments, the isocyanate is selected from methyl isocyanate, ethyl isocyanate, propyl isocyanate, phenyl isocyanate, cyclohexyl isocyanate, 1,4-butanediisocyanate, 1,5-pentanediisocyanate (PDI), hexamethylene diisocyanate (HDI), cyclohexanedimethylene diisocyanate (HXDI), 1,5-diisocyanato-2-methylpentane, 1,4-diisocyanatecyclohexane (CHDI), isophorone diisocyanate (IPDI), isophthalimide diisocyanate (XDI), 4,4'-dicyclohexylmethane diisocyanate (H12MDI), toluene diisocyanate (TDI), diphenylmethane diisocyanate (MDI), terephthalic diisocyanate (PPDI), 1,5-naphthalene diisocyanate (NDI), methylcyclohexane diisocyanate (HTDI), and trimethylhexanediisocyanate (TMD). I) Tetramethyl-methylene diisocyanate (TMXDI), dimethyl biphenyl diisocyanate (TODI), norbornane dimethyl isocyanate (NBDI), 1,8-diisocyanate-4-isocyanate methyl octane, nonane triisocyanate, 2-tetrahydrofuran isocyanate, polyphenyl polymethylene polyisocyanate, 1-isocyanate-1-methyl-4(3)-isocyanate methylcyclohexane (AMCI) Triisocyanate cyclohexane, tri(isocyanate methyl)cyclohexane, triisocyanate methylcyclohexane, 1,8-diisocyanate-4-(isocyanate methyl)octane, undecane 1,6,11-triisocyanate, 1,7-diisocyanate-4-(3-isocyanate propyl)heptane, 1,6-diisocyanate-3-(isocyanate methyl)hexane, or 1,3,5-tri(isocyanate methyl)cyclohexane.

[0037] In some embodiments, the isocyanate is hexamethylene diisocyanate.

[0038] Accordingly, in some embodiments, the amine raw material in the phosgene process is selected from methylamine, ethylamine, propylamine, aniline, cyclohexylamine, 1,4-butanediamine, 1,5-pentanediamine (PDA), 1,6-hexanediamine (HDA), 1,3-cyclohexanedimethylamine (HXDA), 1,5-diamino-2-methylpentane, 1,4-diaminocyclohexane, isophorone diamine (IPDA), m-phenylenediethylene diamine (XDA), 4,4'-diaminodicyclohexylmethanediamine (H12MDA), diphenylmethanediamine (MDA), 2,4 or 2,6-toluenediamine (TDA), diaminobenzene, naphthyldiamine, methylcyclohexanediamine (HTDA), trimethyl... Hexamethylenediamine, tetramethylmethylenediamine, dimethylbiphenyldiamine, norbornene dimethylamine, 1,8-diamino-4-(aminomethyl)octane, triaminononane, 2-tetrahydrofuranamine, polyphenyl polymethylene polyamine, 1-amino-1-methyl-4(3)-aminomethylcyclohexane (AMCA), triaminocyclohexane, tri(aminomethyl)cyclohexane, triaminomethylcyclohexane, 1,8-diamino-4-(aminomethyl)octane, undecane-1,6,11-triamine, 1,7-diamino-4-(3-aminopropyl)heptane, 1,6-diamino-3-(aminomethyl)hexane or 1,3,5-tri(aminomethyl)cyclohexane.

[0039] In some embodiments, the hydrolyzed chlorine content of the crude isocyanate product is 300–1000 ppm, preferably 400–600 ppm.

[0040] In this invention, the hydrolyzable chlorine content refers to the residual hydrolyzable chlorinated byproducts in the product caused by various chlorine-containing impurities such as carbamoyl chloride and dissolved phosgene. This content can be obtained by testing the methods described in the embodiments of this application. It can characterize the level of chlorine-containing impurities in isocyanate products.

[0041] In some embodiments, after hydrodechlorination, the crude isocyanate product has a hydrolyzed chlorine content of 80–200 ppm, preferably 80–150 ppm. It is evident that the method of this application can significantly reduce the chlorine impurity content in the crude isocyanate product.

[0042] In some embodiments, the acidity of the crude isocyanate product is 150–500 ppm, preferably 150–200 ppm.

[0043] In some embodiments, the crude isocyanate product, after undergoing a hydrodechlorination reaction, has an acidity of 30–100 ppm, preferably 30–65 ppm.

[0044] The present invention also provides a method for preparing isocyanate by phosgene method, comprising the step of reacting amine and phosgene as raw materials in a reactor to prepare crude isocyanate product, and the step of removing phosgene and solvent from the crude isocyanate product. The method further includes the step of performing the aforementioned method for reducing chlorine impurities in isocyanate on the crude isocyanate product after solvent removal.

[0045] In the phosgene process, the gas-phase phosgene method uses amines and phosgene (gaseous), while the liquid phosgene method uses solutions of amines and phosgene. Because the gas-phase phosgene method typically involves cooling the reaction system with a large amount of solvent after synthesis, the various chlorine-containing impurities produced by both methods are usually in liquid form. The choice between gas-phase and liquid phosgene methods has no impact on subsequent methods for reducing chlorine-containing impurities.

[0046] In some embodiments, the method for preparing isocyanates by the phosgene process further includes a step of purifying the crude isocyanate product after the hydrodechlorination reaction step.

[0047] Furthermore, the purification may include, for example, distillation to remove light component impurities, and byproduct removal to remove heavy component impurities.

[0048] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0049] This application involves a hydrodechlorination reaction of crude isocyanate with hydrogen in the presence of a catalyst. This allows chlorine-containing impurities in the crude product, such as carbamoyl chloride and chlorinated aromatics, to react with hydrogen to generate chlorine-free organic compounds and HCl. Furthermore, the catalyst composition is chosen to adsorb HCl gas, further shifting the hydrodechlorination reaction in the forward direction and reducing the content of chlorine-containing impurities. Simultaneously, it also reduces the acidity of the isocyanate product. This method for reducing chlorine-containing impurities in isocyanate does not require the introduction of other treatment agents, does not introduce new impurities, and uses a heterogeneous catalyst, making it easy to separate from the reaction system.

[0050] This application selects a specific catalyst support and adds auxiliary components in addition to the active components, so that the catalyst forms a bimetallic active center, which significantly improves the efficiency and stability of its catalytic hydrodechlorination reaction. It can further reduce the chlorine impurities in the crude isocyanate product and further reduce the hydrolytic chlorine content and acidity of the treated isocyanate.

[0051] Using the method of this application, the hydrolyzed chlorine content of crude isocyanate products can reach 80-200 ppm after hydrodechlorination. Attached Figure Description

[0052] Figure 1 This is a schematic flowchart of the method for preparing isocyanates by the phosgene method of the present invention. Detailed Implementation

[0053] The technical solutions of the present invention will be described in detail below with reference to specific embodiments, so that those skilled in the art can better understand and implement the technical solutions of the present invention, but the present invention is not limited to the scope of the examples described.

[0054] Preparation Example 1

[0055] Synthesis catalyst:

[0056] A certain amount of palladium chloride and silver nitrate were dissolved in water to prepare a metal precursor solution. A certain amount of DiaionPA308 quaternary ammonium type strong basic anion exchange resin was dispersed in the aforementioned metal precursor solution. The mixture was stirred and impregnated for 3 hours at room temperature. Sodium borohydride was added, and stirring was continued to ensure that the metal particles were completely reduced. The mixture was then centrifuged and filtered, washed multiple times with ethanol, dried under vacuum, and stored under inert gas conditions to obtain a Pd-Ag / Diaion PA308 catalyst with a Pd content of 0.45 wt% and an Ag content of 1.3 wt%. Its composition is shown in Table 1 below.

[0057] Preparation Examples 2-8

[0058] Catalyst Synthesis: The synthesis steps are basically the same as in Example 1, with the only differences being the type of support resin, the precursors of the active component and the auxiliary agent, and the amounts of each component. Specifically, the precursor for the auxiliary agent Cu is copper nitrate, the precursor for Sn is tin nitrate, the precursor for the active component Pt is chloroplatinic acid, and the precursor for the active component Ni is nickel nitrate. The obtained catalysts and their corresponding compositions are shown in Table 1 below.

[0059] Comparative Preparation Example 1

[0060] Synthetic catalyst: The synthesis steps are basically the same as those in Preparation Example 1, except that: no precursors are added and the catalyst does not contain any additives, as shown in Table 1 below.

[0061] Comparative Preparation Example 2

[0062] Synthesis of catalyst: The synthesis steps are basically the same as those in Preparation Example 1, except that the support is replaced by Diaion PA308 quaternary ammonium strong base anion exchange resin with guanidine strong base anion exchange resin (which does not have quaternary ammonium functional groups) (its preparation method is the same as described in Section 2.1.2.2 Synthesis of Guanidine Resin in Zan Huining's "Synthesis and Performance Study of Novel High Temperature Resistant Guanidine Strong Base Resin", Nankai University Doctoral Dissertation, where the feeding ratio of chloromethylated polystyrene gel resin to free guanidine is 1:3), as shown in Table 1 below.

[0063] Table 1 Catalyst composition

[0064] Preparation Example Catalyst code Active ingredient content / wt% Additive content / wt% Preparation Example 1 Pd-Ag / Diaion PA308 0.45 1.3 Preparation Example 2 Pd-Ag / Diaion PA308 0.70 1.3 Preparation Example 3 Pd-Cu / Diaion PA308 0.45 0.8 Preparation Example 4 Pd-Sn / Diaion PA308 0.45 1.4 Preparation Example 5 Pd-Ag / Dowex MSA-1 0.45 1.3 Preparation Example 6 Pd-Ag / Lewait MP 500 0.45 1.3 Preparation Example 7 Pt-Ag / Diaion PA308 0.72 1.3 Preparation Example 8 Ni-Ag / Diaion PA308 0.25 1.3 Comparative Preparation Example 1 Pd / Diaion PA308 0.45 none Comparative Preparation Example 2 Pd-Ag / Guidinyl Resin 0.45 1.3

[0065] Examples 1-8, Comparative Examples 1-2

[0066] The catalysts prepared in Preparation Examples 1-8 and Comparative Preparation Examples 1-2 were used in the method of this application, as follows:

[0067] like Figure 1 As shown, after the reaction of hexamethylenediamine and phosgene in the phosgenation reactor is completed, the product enters a dephosgene tower to recover excess phosgene. The liquid material enters a desolventizing tower to recover excess solvent. The crude product after desolventizing enters a hydrodechlorination reactor, which is a fixed-bed reactor filled with the aforementioned catalysts. The crude isocyanate product after desolventizing and hydrogen enter from the bottom of the reactor. The reaction temperature is 70°C, the pressure is 2 MPa, and the catalyst volume hourly space velocity is 1500 h⁻¹. -1 The mass ratio of crude isocyanate to hydrogen is 2500. The liquid material enters the subsequent product refining process for purification (including distillation, etc.). Excess hydrogen is recycled, and hexamethylene diisocyanate is finally obtained. The hydrolyzed chlorine content and acidity content in the crude isocyanate product, as well as the hydrolyzed chlorine content and acidity content of the crude product after hydrodechlorination (product from the hydrodechlorination reactor), are detected by the following methods: Acidity detection refers to (GB / T 12009.5-2016), and the method for detecting hydrolyzed chlorine content is as follows:

[0068] 1) Method Summary

[0069] Hydrolyzed chlorine mainly originates from carbamoyl chloride and dissolved phosgene generated during the production process. These two substances react with alcohol and water to produce urea, carbamates, carbon dioxide, and hydrochloric acid. The hydrochloric acid produced is determined by potentiometric titration with silver nitrate standard solution.

[0070] 2) Reagents and Materials

[0071] Anhydrous methanol and acetone;

[0072] Nitric acid solution: Prepared by mixing nitric acid (65%–68%) and water in a volume ratio of 1:3;

[0073] Sodium chloride solution: C(NaCl) = 100 mg / L;

[0074] Silver nitrate standard solution: C(AgNO3)=0.01mol / L.

[0075] 3) Instruments and equipment

[0076] Automatic potentiometric titrator, equipped with a silver-silver chloride electrode;

[0077] Laboratory heating equipment;

[0078] Reflux condenser;

[0079] Laboratory glassware.

[0080] 4) Test Procedure

[0081] Weigh 9g to 11g (accurate to 0.01g) of sample (4g to 6g is recommended if the hydrolyzed chlorine content is greater than 50mg / kg), put it into a clean and dry 300mL Erlenmeyer flask, add 100mL of methanol, install a reflux condenser, stir, and heat to a gentle boil, maintain reflux for 10min to ensure complete alcoholysis.

[0082] Add 50 mL of water to the reflux condenser;

[0083] Stir and heat under reflux for 30 minutes;

[0084] Add 20 mL of acetone, cool to room temperature, transfer to 10.00 mL of sodium chloride solution, and add 10 mL of nitric acid solution;

[0085] Potentiometric titration was performed using a standard silver nitrate solution.

[0086] At the same time, a blank test was performed.

[0087] 5) Expression of test results

[0088] calculate:

[0089] The hydrolyzable chlorine content (w2) of HDI, expressed in milligrams per kilogram (mg / kg), is calculated using the following formula:

[0090]

[0091] In the formula:

[0092] w2 — Content of hydrolyzed chlorine, in milligrams per kilogram (mg / kg);

[0093] V — The volume of silver nitrate standard solution consumed during sample titration, in milliliters (mL);

[0094] V0 — The volume of silver nitrate standard solution consumed during blank titration, in milliliters (mL);

[0095] c — the actual concentration of the silver nitrate standard solution, in moles per liter (mol / L);

[0096] M – Molar mass of chlorine, in grams per mole (g / mol) (M = 35.4 g / mol);

[0097] m — the mass of the sample, in grams (g).

[0098] The results are expressed as the arithmetic mean of two repeated measurements.

[0099] Repeatability: The absolute value of the difference between two parallel determinations is not greater than 5 mg / kg.

[0100] The results are shown in Table 2 below.

[0101] Table 2 Results of hydrodechlorination treatment

[0102]

[0103] As shown in Table 2 above, by selecting an alkaline anion exchange resin with quaternary ammonium functional groups as the support for the hydrodechlorination catalyst and adding auxiliary metals to the active components, the present invention can further reduce the content of chlorine impurities and acidity of crude isocyanate products.

[0104] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for reducing chlorine-containing impurities in isocyanates, characterized in that: The method includes a step of hydrodechlorinating a crude isocyanate product obtained by the phosgene method with hydrogen in the presence of a catalyst. The crude isocyanate product contains chlorine impurities. The catalyst is a supported catalyst and includes a support, an active component, and an auxiliary agent. The combination of the active component and the auxiliary agent is Pd-Ag, Pd-Cu, Pd-Sn, Pt-Ag, or Ni-Ag. The carrier is selected from one or more of Diaion PA308 resin, Dowex MSA-1 resin and Lewait MP 500 resin; The catalyst contains 0.01% to 3% active components and 0.03% to 8% additives by mass percentage.

2. The method for reducing chlorine impurities in isocyanates according to claim 1, characterized in that: The catalyst contains 0.05% to 2% active components and 0.1% to 5% additives by mass percentage.

3. The method for reducing chlorine impurities in isocyanates according to claim 1, characterized in that: The hydrodechlorination reaction is carried out in a reactor, which is selected from a batch reactor, a fixed bed reactor, a fluidized bed reactor, or a tower reactor.

4. The method for reducing chlorine-containing impurities in isocyanates according to claim 3, characterized in that: The reactor is a fixed bed reactor, the volume space velocity of the catalyst is 500~2000 h -1 .

5. The method for reducing chlorine-containing impurities in isocyanates according to claim 3, characterized in that: The reactor is selected from a batch reactor, a fluidized bed reactor, or a tower reactor, and the mass of the catalyst is 0.05% to 2% of the mass of the crude isocyanate product.

6. The method for reducing chlorine-containing impurities in isocyanates according to claim 1, characterized in that: The temperature of the hydrodechlorination reaction is 50~150 ℃.

7. The method for reducing chlorine-containing impurities in isocyanates according to claim 1, characterized in that: The mass ratio of the crude isocyanate product to hydrogen is 10000:1 to 1000:

1.

8. The method for reducing chlorine-containing impurities in isocyanates according to claim 1, characterized in that: The isocyanate is selected from aliphatic or aromatic isocyanates.

9. The method for reducing chlorine-containing impurities in isocyanates according to claim 1, characterized in that: The isocyanate is selected from methyl isocyanate, ethyl isocyanate, propyl isocyanate, phenyl isocyanate, cyclohexyl isocyanate, 1,4-butanediisocyanate, 1,5-pentanediisocyanate, hexamethylene diisocyanate, cyclohexanedimethyl diisocyanate, 1,5-diisocyanato-2-methylpentane, 1,4-diisocyanate cyclohexane, isophorone diisocyanate, isophthalic diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, toluene diisocyanate, diphenylmethane diisocyanate, terephthalic diisocyanate, 1,5-naphthalene diisocyanate, methylcyclohexane diisocyanate, trimethylhexanediisocyanate, tetramethyl isophthalic diisocyanate, dimethyl biphenyl diisocyanate, norbornene diisocyanate, and 1,8-diisocyanate-4-isocyanate. Methyl octane, nonane triisocyanate, 2-tetrahydrofuran isocyanate, polyphenyl polymethylene polyisocyanate, 1-isocyano-1-methyl-4(3)-isocyano-methylcyclohexane, triisocyano-cyclohexane, tri(isocyano-methyl)cyclohexane, triisocyano-methylcyclohexane, 1,8-diisocyano-4-(isocyano-methyl)octane, undecane 1,6,11-triisocyanate, 1,7-diisocyano-4-(3-isocyano-propyl)heptane, 1,6-diisocyano-3-(isocyano-methyl)hexane or 1,3,5-tri(isocyano-methyl)cyclohexane.

10. The method for reducing chlorine-containing impurities in isocyanates according to claim 1, characterized in that: The crude isocyanate product has a hydrolyzable chlorine content of 300-1000 ppm; and / or, after hydrodechlorination, the crude isocyanate product has a hydrolyzable chlorine content of 80-150 ppm; and / or, the crude isocyanate product has an acidity of 150-500 ppm; and / or, after hydrodechlorination, the crude isocyanate product has an acidity of 30-65 ppm.

11. A method for preparing isocyanate by phosgene reaction, comprising the steps of reacting amine and phosgene as raw materials in a reactor to prepare crude isocyanate product, and the steps of removing phosgene and solvent from the crude isocyanate product, characterized in that: The method further includes the step of performing the method for reducing chlorine-containing impurities in the isocyanate as described in any one of claims 1-10 on the crude isocyanate product after solvent removal.

12. The method for preparing isocyanate by phosgene method according to claim 11, characterized in that: The method further includes a step of purifying the crude isocyanate product after the hydrodechlorination reaction step.

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